General Anesthesia Practice Questions

Q: What is the chemical formula for laughing gas?

N2O. **Explanation:** **Nitrous Oxide (N₂O)**, commonly known as **laughing gas**, is the correct answer. It is a colorless, odorless, and non-flammable inorganic gas used in anesthesia for its analgesic and sedative properties. It acts primarily by inhibiting NMDA receptors and stimulating opioid neurons in the brain. **Analysis of Options:** * **A. N₂O (Correct):** This is the chemical formula for Nitrous Oxide. It is the only inorganic gas used in modern clinical anesthesia. * **B. Lewisite:** This is an organoarsenic compound used as a chemical weapon (blister agent/vesicant). It is not used in anesthesia. * **C. H₂S (Hydrogen Sulfide):** A highly toxic, flammable gas with a characteristic "rotten egg" smell. It is a potent cellular asphyxiant. * **D. CO₂ (Carbon Dioxide):** While used in medicine (e.g., for insufflation during laparoscopy), it is a byproduct of metabolism and not an anesthetic agent. **High-Yield Clinical Pearls for NEET-PG:** 1. **Blood-Gas Partition Coefficient:** N₂O has a low coefficient (0.47), leading to rapid induction and recovery. 2. **Second Gas Effect:** N₂O accelerates the uptake of a co-administered volatile anesthetic. 3. **Diffusion Hypoxia (Fink Effect):** Occurs at the end of surgery when N₂O rapidly diffuses from blood to alveoli, diluting oxygen. Prevention requires 100% O₂ for 5–10 minutes post-discontinuation. 4. **Contraindications:** Because N₂O is 34 times more soluble than Nitrogen, it expands closed air spaces. It is strictly contraindicated in **pneumothorax, intestinal obstruction, air embolism, and middle ear surgeries.** 5. **Vitamin B12:** Chronic exposure inhibits methionine synthase, leading to megaloblastic anemia and peripheral neuropathy.

Q: Which intravenous anesthetic agent possesses local anesthetic properties?

Ketamine. **Explanation:** **Ketamine** is a unique phencyclidine derivative that acts primarily as an NMDA receptor antagonist. Beyond its systemic effects, ketamine possesses significant **local anesthetic properties**. It exerts this effect by blocking sodium channels in a manner similar to conventional local anesthetics (like Lidocaine). When applied topically or injected locally, it can produce sensory blockade. Clinically, this property is sometimes utilized in "multimodal analgesia" to reduce postoperative pain. **Analysis of Incorrect Options:** * **Propofol:** An alkylphenol that acts via GABA-A receptors. It is notorious for causing **pain on injection** (due to activation of the kinin system), which is the opposite of a local anesthetic effect. * **Thiopentone:** A short-acting barbiturate. It is actually considered **anti-analgesic** in sub-anesthetic doses, meaning it can lower the pain threshold. Accidental intra-arterial injection causes severe vasospasm and necrosis, not anesthesia. * **Etomidate:** An imidazole derivative used for its cardiovascular stability. It has no analgesic or local anesthetic properties and is associated with myoclonus and adrenocortical suppression. **High-Yield Clinical Pearls for NEET-PG:** * **Dissociative Anesthesia:** Ketamine causes a state where the patient appears awake (eyes open) but is unconscious and amnesic. * **Sympathomimetic:** It is the IV anesthetic of choice for **bronchial asthma** and **hypovolemic shock** because it increases HR, BP, and causes bronchodilation. * **Contraindications:** Avoid in patients with raised Intracranial Pressure (ICP) or Intraocular Pressure (IOP), and those with ischemic heart disease. * **Emergence Delirium:** A common side effect characterized by hallucinations, which can be prevented by pre-treating with Benzodiazepines (e.g., Midazolam).

Q: Succinylcholine is a/an

None of the above. **Explanation:** The correct answer is **D. None of the above** because Succinylcholine (Suxamethonium) is a **depolarizing neuromuscular blocking agent**. It is the only drug in this class currently used in clinical practice. **Why the options are incorrect:** * **Option A:** Succinylcholine is not an anesthetic agent; it provides no analgesia or unconsciousness. It is a muscle relaxant used to facilitate endotracheal intubation. * **Option B:** Succinylcholine is a **depolarizing** relaxant. It acts as an agonist at the nicotinic acetylcholine receptors (nAChR) at the neuromuscular junction, causing persistent depolarization (manifested as fasciculations) followed by flaccid paralysis. Non-depolarizing agents (e.g., Vecuronium, Atracurium) act as competitive antagonists. * **Option C:** It is not a narcotic (opioid). It has no effect on pain pathways or opioid receptors. **High-Yield NEET-PG Pearls:** 1. **Mechanism:** It mimics acetylcholine but is not degraded by acetylcholinesterase; it is metabolized by **Pseudocholinesterase** (Butyrylcholinesterase). 2. **Onset and Duration:** It has the fastest onset (30–60 seconds) and shortest duration (5–10 minutes), making it the drug of choice for **Rapid Sequence Induction (RSI)**. 3. **Key Side Effects:** Hyperkalemia (avoid in burns, trauma, or denervation injuries), muscle fasciculations, myalgia, and increased intraocular/intragastric pressure. 4. **Malignant Hyperthermia:** Succinylcholine is a known trigger for Malignant Hyperthermia (treated with Dantrolene). 5. **Phase II Block:** Prolonged exposure or high doses can lead to a Phase II block, where the membrane repolarizes but remains insensitive to acetylcholine, behaving like a non-depolarizing block.

Q: Non-depolarizing muscle relaxants are potentiated by all except?

Phenytoin. **Explanation:** The potentiation or antagonism of non-depolarizing muscle relaxants (NDMRs) depends on their interaction with the neuromuscular junction (NMJ) and hepatic enzyme induction. **Why Phenytoin is the correct answer:** Phenytoin is a potent **hepatic enzyme inducer**. Chronic administration of phenytoin (and carbamazepine) leads to an increased rate of metabolism of NDMRs (especially vecuronium and rocuronium). Furthermore, it causes an up-regulation of acetylcholine receptors at the NMJ. Both mechanisms lead to **resistance** to NDMRs, meaning higher doses are required and the duration of action is shortened. Therefore, it does not potentiate but rather **antagonizes** the effect. **Why the other options are incorrect:** * **Aminoglycosides (e.g., Neomycin, Gentamicin):** These potentiate NDMRs by inhibiting the pre-junctional release of Acetylcholine (ACh) and reducing post-junctional sensitivity to ACh. * **Polymyxins:** These exert a potent neuromuscular blocking effect by acting like "membrane stabilizers," significantly prolonging the block. * **Quinidine:** This Class IA antiarrhythmic potentiates NDMRs by depressing muscle fiber excitability and decreasing ACh release. **High-Yield Clinical Pearls for NEET-PG:** * **Antibiotics that potentiate NDMRs:** Aminoglycosides, Tetracyclines, Polymyxin, and Lincomycin. (Note: Penicillins and Cephalosporins do **not** have this effect). * **Electrolytes that potentiate NDMRs:** Hypokalemia, Hypermagnesemia, and Hypocalcemia. * **Other potentiators:** Inhalational anesthetics (Desflurane > Sevoflurane > Isoflurane), Local anesthetics, and Hypothermia. * **Acute vs. Chronic Phenytoin:** While chronic use causes resistance, an *acute* IV dose of phenytoin can occasionally potentiate the block. However, for exam purposes, Phenytoin is the classic example of resistance/antagonism.

Q: Which of the following is NOT an intravenous anesthetic agent?

Cyclopropane. **Explanation:** The correct answer is **Cyclopropane** because it is an **inhalational (volatile) anesthetic gas**, not an intravenous agent. Historically used for its rapid induction and maintenance of blood pressure, it has been largely phased out in modern practice due to its high flammability and explosive potential when mixed with oxygen. **Analysis of Options:** * **Etomidate (Option A):** An intravenous induction agent known for its **cardiovascular stability**. It is the drug of choice for hemodynamically unstable patients or those with coronary artery disease. A key side effect is transient adrenal suppression. * **Thiopentone (Option B):** A classic ultra-short-acting **barbiturate** administered intravenously. It was the gold standard for rapid induction for decades. It is contraindicated in patients with porphyria. * **Ketamine (Option C):** An intravenous agent that produces **dissociative anesthesia**. It is unique because it provides potent analgesia and stimulates the sympathetic nervous system, making it useful in hypovolemic shock and asthma. **NEET-PG High-Yield Pearls:** * **Propofol** is currently the most commonly used IV induction agent ("Milk of Amnesia"). * **Cyclopropane** is known for the "Cyclopropane Shock" (post-operative hypotension) and sensitizing the myocardium to catecholamines, leading to arrhythmias. * **Drug of Choice (DOC) Summary:** * Day-care surgery: Propofol * Shock/Trauma: Ketamine or Etomidate * Head injury (to decrease ICP): Thiopentone or Propofol

Q: Minimum alveolar concentration (MAC) of an anesthetic agent means it produces lack of reflex response to skin incision in what percentage of subjects?

50%. **Explanation:** The **Minimum Alveolar Concentration (MAC)** is a fundamental concept in inhalational anesthesia, representing the potency of an anesthetic agent. It is defined as the steady-state alveolar concentration of an anesthetic gas (at 1 atmosphere) that prevents gross purposeful movement in response to a standard surgical stimulus (skin incision) in **50% of subjects**. **Why 50% is Correct:** MAC is essentially the **ED50** (Median Effective Dose) for inhalational agents. It provides a standardized measure to compare the potency of different gases; the lower the MAC value, the more potent the anesthetic (e.g., Halothane has a MAC of 0.75%, while Nitrous Oxide is >100%). **Why Other Options are Incorrect:** * **25% (Option A):** This value does not correspond to any standard clinical definition of anesthetic potency. * **75% (Option C):** While higher concentrations increase the depth of anesthesia, 75% is not the statistical benchmark used for MAC. * **100% (Option D):** To ensure 95-99% of patients do not move, clinicians use **MAC-BAR** (Blunt Autonomic Response) or roughly **1.3 MAC**, which is the surgical dose required for most clinical procedures. **High-Yield Clinical Pearls for NEET-PG:** * **MAC-Awake:** The concentration at which 50% of patients respond to verbal commands (usually ~0.3–0.4 MAC). * **Factors that INCREASE MAC (Require more gas):** Hyperthermia, hypernatremia, chronic alcohol abuse, and increased central neurotransmitters (e.g., cocaine, ephedrine). * **Factors that DECREASE MAC (Require less gas):** Hypothermia, pregnancy, acute alcohol intoxication, old age, and concurrent use of opioids or benzodiazepines. * **Meyer-Overton Hypothesis:** States that MAC is inversely proportional to lipid solubility (Oil:Gas partition coefficient).

Q: Which of the following is NOT true regarding neurolept analgesia?

None of the above. **Explanation:** **Neuroleptanalgesia (NLA)** is a state of profound sedation and analgesia produced by the combination of an opioid analgesic and a neuroleptic (antipsychotic) drug. The classic combination used is **Fentanyl** (opioid) and **Droperidol** (butyrophenone neuroleptic). 1. **Why Option D is correct:** All the statements (A, B, and C) are medically accurate descriptions of neuroleptanalgesia. Since the question asks for the statement that is **NOT** true, "None of the above" is the correct choice. 2. **Analysis of Options:** * **Option A:** NLA can indeed be used with **O₂ and N₂O**. When these inhalation gases are added to the fentanyl-droperidol combination, the state is upgraded to **Neurolept anesthesia**, which provides complete unconsciousness suitable for surgery. * **Option B:** Droperidol is a dopamine (D2) receptor antagonist. Like other antipsychotics, it can cause **extrapyramidal side effects**, most notably **focal dystonia** (e.g., oculogyric crisis or torticollis). * **Option C:** The combination of **Fentanyl and Droperidol** (commercially known as Innovar in a 1:50 ratio) is the prototype example of neuroleptanalgesia. **High-Yield Clinical Pearls for NEET-PG:** * **Innovar Ratio:** Contains 0.05 mg Fentanyl and 2.5 mg Droperidol per mL. * **Patient State:** The patient remains conscious, detached from surroundings, and cooperative but feels no pain (quiescence). * **Contraindication:** Avoid in patients with **Parkinson’s disease** due to the dopamine-blocking effects of droperidol. * **Side Effects:** Droperidol can cause **QT interval prolongation**; therefore, ECG monitoring is recommended.

Q: Which of the following is a common side effect of ketamine?

Emergence delirium. **Explanation:** **Ketamine** is a unique intravenous anesthetic agent that acts as an NMDA receptor antagonist, producing a state known as **dissociative anesthesia**. **1. Why Emergence Delirium is Correct:** Emergence delirium (or emergence reactions) is the most characteristic side effect of ketamine. As the patient recovers from anesthesia, they may experience vivid dreams, hallucinations, illusions, and confusion. This occurs due to the depression of sensory association areas in the brain while the limbic system remains active. It is more common in adults than children and can be minimized by pre-medication with **benzodiazepines** (e.g., Midazolam). **2. Why the Other Options are Incorrect:** * **B. Pain on injection:** This is a classic side effect of **Propofol** and **Etomidate**, not Ketamine. * **C. Bronchoconstriction:** Ketamine is actually a potent **bronchodilator** due to its sympathomimetic effects. It is the induction agent of choice for patients with status asthmaticus. * **D. Depression of cardiovascular system:** Unlike most anesthetics, Ketamine **stimulates** the cardiovascular system (increasing HR, BP, and CO) via indirect sympathetic stimulation. It is the agent of choice for patients in **hypovolemic shock**. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** NMDA receptor antagonist. * **Analgesia:** Provides profound somatic analgesia. * **Reflexes:** Airway reflexes (cough/gag) are usually preserved. * **Contraindications:** Head injury (increases ICP), Intraocular surgery (increases IOP), and Ischemic Heart Disease (increases myocardial oxygen demand). * **Secretions:** Causes significant **hypersalivation**; often co-administered with Glycopyrrolate.

Question 1

What is the chemical formula for laughing gas?

Accepted Answer

N2O

Answer

Lewisite

Answer

H2S

Answer

CO2

Question 2

Which of the following fluorinated anesthetic agents does not produce toxic fluoride ions?

Accepted Answer

Desflurane

Answer

Sevoflurane

Answer

Methoxyflurane

Answer

Enflurane

Question 3

Which intravenous anesthetic agent possesses local anesthetic properties?

Accepted Answer

Ketamine

Answer

Propofol

Answer

Thiopentone

Answer

Etomidate

Question 4

Succinylcholine is a/an

Accepted Answer

None of the above

Answer

Intravenous anesthetic agent

Answer

Non-depolarizing muscle relaxant

Answer

Short-acting narcotic

Question 5

Non-depolarizing muscle relaxants are potentiated by all except?

Accepted Answer

Phenytoin

Answer

Aminoglycoside antibiotics

Answer

Polymyxin

Answer

Quinidine

Question 6

Which of the following is NOT an intravenous anesthetic agent?

Accepted Answer

Cyclopropane

Answer

Etomidate

Answer

Thiopentone

Answer

Ketamine

Question 7

Which of the following inhalation anesthetics causes rapid induction of anesthesia?

Accepted Answer

Halothane

Answer

Isoflurane

Answer

Desflurane

Answer

Sevoflurane

Question 8

Minimum alveolar concentration (MAC) of an anesthetic agent means it produces lack of reflex response to skin incision in what percentage of subjects?

Accepted Answer

50%

Answer

25%

Answer

75%

Answer

100%

Question 9

Which of the following is NOT true regarding neurolept analgesia?

Accepted Answer

None of the above

Answer

Can be used along with O2 and N2O

Answer

Causes focal dystonia

Answer

Is exemplified by Fentanyl-droperidol

Question 10

Which of the following is a common side effect of ketamine?

Accepted Answer

Emergence delirium

Answer

Pain on injection

Answer

Bronchoconstriction

Answer

Depression of cardiovascular system

General Anesthesia — MCQs

General Anesthesia — MCQs

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